"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
iMac, iPhone References Found In Mac OS 10.4.10 Update
Forum member bogg writes that four new display vendor ID's appear in 10.4.10 relating to the iMac. While the ID's themselves do not suggest any specific features of the iMac, they do lend credence to rumors that Apple plans to update the product within the next several weeks.
Also, AppleInsider reports that a new framework named "YahooSync" is installed with the update, most likely referring to support for various Yahoo! services supported by the the iPhone (including push IMAP and Yahoo! address books).
Meanwhile, forum user milhous, notes that http://www.yahoo.com/iphone redirects to http://iphone.yahoo.com with a "Sorry, the page you requested was not found" error. The DNS changes suggest that Yahoo may be preparing their own iPhone portal.